1. Field of the Invention
The present invention relates generally to an inflator for an air bag or the like and, more specifically, to a compact dual nozzle inflator which can selectively release gas at different rates and levels and thus enable an air bag to be deployed at different output levels in accordance with different sensor inputs.
2. Description of the Related Art
Recently, there has been a demand for controlling the rate and amount of inflation of safety devices such as air bag restraint systems in accordance with variables such as passenger size, position, seat belt usage and the velocity of a vehicle at the time of collision.
In order to provide optimal occupant protection, different levels of output are required from the airbag inflator. For example, in a high speed collision with a large belted person, full rapid inflation of the air bag is required to provide the best restraint. In lower speed crashes with smaller sized occupants or even out-of-position position occupants, a lower, slower rate of inflation is required so as not to inadvertently injure the occupant but still provide enough inflation to effect appropriate restraint.
In currently available air bag inflators intended for dual level or variable output function, the performance is accomplished primarily with inflators which are made up of two individual inflators sharing one diffuser, or by individual propellant chambers in a common pressure vessel sharing one common nozzle.
Utilizing two separate inflators results in large, heavy and expensive designs since nearly every component is duplicated. For example, there are two distinct pressure vessels, with redundant closures, seals, and in some cases diffusers. Additionally, there is the added requirement of securing the two inflators to a common platform, which in turn increases cost, weight, and complexity in manufacturing. One advantage of such a design is the ability to operate separate nozzles for each of the two inflators. This provides flexibility in functioning the inflators at different times, depending on the output level required, with much more predictable and repeatable performance. Each nozzle is optimized for the specific propellant configuration present in the respective gas generator. One propellant with different geometry, burn rate, and formulation could be used independent of the other to tailor and optimize the inflator performance.
The second approach of having separate propellant chambers encapsulated in one common pressure vessel results in more efficient packaging, and reduced cost if the components are shared by the two propellant charges. However, the primary disadvantage of such construction is that they typically share one common nozzle for all inflator output configurations. For example, a high output inflator deployment requiring simultaneous combustion of both propellant chambers will discharge all of inflator gases from one nozzle geometry. This nozzle is typically optimized for the maximum output condition in order to keep operating pressures within design limits.
Depending on the vehicle crash scenario, a deployment condition requiring something less than full output, i.e., a staggered combustion of the two propellant charges, or combustion of just one apropellant charge, may be initiated. Since the nozzle has been optimized for full output, this reduced output performance will be less than optimum, owing to lower combustion pressure often resulting in poor repeatability, especially across the temperature range. The flexibility to accommodate a wide range of performances with a single nozzle becomes very limited. The problem is further exacerbated with the usage of pressure sensitive, xe2x80x9chigh slopexe2x80x9d propellants such as those based on ammonium nitrate formulations.
Consequently, there is a need for a cost-effective, light-weight, compact, simple multi-level inflator for air bags and the like. This need is met by the new and improved inflator of the present invention.
It is an object of the present invention, therefore, to overcome the disadvantages of the prior art and to provide a cost-effective, light-weight, compact and simple multi-level inflator device which is reliable in operation.
A further object of the present invention is to provide a multi-level inflator with two gas generators, which permits ignition of the generators either separately, simultaneously or in a timed sequence to effect air bag inflation at different rates in accordance with sensor inputs resulting from a crash or the like.
It is a further object of the present invention to provide a multi-level inflator which utilizes a common pressure vessel to provide two separate and distinct propellant chambers with completely independent ignitors and nozzles.
It is an additional object of the present invention to provide such a multi-level inflator which may be of the pyro or hybrid type.
Still another object of the present invention is to provide such a multi-level inflator which is simple in construction and easy to assemble to minimize the cost and size of the assembly.
These and other objects of the present invention are achieved by providing a multi-level inflation device for inflating a vehicle safety restraint such as an air bag comprising a common pressure vessel which is constructed to provide two separate and distinct propellant chambers with independent ignitors. The combustion gases do not communicate between the chambers so that they perform as xe2x80x9cseparatexe2x80x9d inflators which maintaining the size and weight of a comparable single stage inflator. The gases exit from separate nozzles in each chamber into a common diffuser and screen assembly to minimize redundant components. The inflator can be configured as either a variable output pyro inflator or a variable output hybrid inflator with essentially the same components.